For the purpose of the following description, the term "image" will be understood to mean a two dimensional representation that can be sampled digitally and represented by a frame or field containing lines of pixels, where each pixel represents one picture element. The size of an image represented by the number of pixels per line and the number of lines per frame or field may be changed by digital signal processing, without changing the information content of the image.
According to the prior art, various forms of digital signal processing of images are known, such as disclosed in U.S. Pat. Nos. 4,674,125 and 4,797,942. It is well known in the art to generate images which have been filtered, resized, projected, warped, etc. (see Digital Image Warping, George Wolberg, IEEE Computer Society Press 1988; Two-dimensional Signal and Image Processing, Jae S. Lim, Prentice Hall 1990; Handbook of Digital Signal Processing, Douglas F. Elliott, Academic Press 1987).
It is also well known that digital image processors, such as filters, can be implemented via integrated circuits. These circuits are limited in the sizes of images that can be processed thereby within a given time frame because of maximum clock rates and by the sizes of the elements used to provide line delays in such circuits. Software implementations are similarly limited by the maximum throughput of the CPU that is used to run the software.
U.S. patent application Ser. No. 07/766,128 abandoned, continuation-in-part application No. 08/033,503 filed Mar. 18, 1993, now issued to U.S. Pat. No. 5,355,328) describes, in general terms, an apparatus for providing an image resizing function. The first element in the apparatus disclosed in application Ser. No. 07/766,128 is an interpolator for changing the number of samples of an input sample stream having a given sampling period P by a factor of M/CL, where C is a positive integer and M is smaller than CL, and where either 2.sup.n M/CL or 2.sup.-n M/CL is equal to the time increment M/L and the absolute value of n is at least equal to zero, so that the sampling period of the first derived sample stream is (M/(CL))P.
The second element in the apparatus disclosed in application Ser. No. 07/766,128 is an octave filtering means having a predetermined sampling rate which is related to the interpolation rate of the first element so that the output of the second element has a sample period of (M/L) P.